Bandwidth sensitive data compression and decompression

ABSTRACT

Data compression and decompression methods for compressing and decompressing data based on an actual or expected throughput (bandwidth) of a system. In one embodiment, a controller tracks and monitors the throughput (data storage and retrieval) of a data compression system and generates control signals to enable/disable different compression algorithms when, e.g., a bottleneck occurs so as to increase the throughput and eliminate the bottleneck.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of commonly-assigned U.S. patent application Ser.No. 10/076,013, filed Feb. 13, 2002, now U.S. Pat. No. 7,386,046, whichclaims the benefit of U.S. Provisional Patent Application No.60/268,394, filed Feb. 13, 2001, each of which is fully incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present invention relates generally to data compression anddecompression and, in particular, to a system and method for compressingand decompressing data based on an actual or expected throughput(bandwidth) of a system that employs data compression. Additionally thepresent invention relates to the subsequent storage, retrieval, andmanagement of information in data storage devices utilizing eithercompression and/or accelerated data storage and retrieval bandwidth.

2. Description of Related Art

There are a variety of data compression algorithms that are currentlyavailable, both well defined and novel. Many compression algorithmsdefine one or more parameters that can be varied, either dynamically ora-priori, to change the performance characteristics of the algorithm.For example, with a typical dictionary based compression algorithm suchas Lempel-Ziv, the size of the dictionary can affect the performance ofthe algorithm. Indeed, a large dictionary may be employed to yield verygood compression ratios but the algorithm may take a long time toexecute. If speed were more important than compression ratio, then thealgorithm can be limited by selecting a smaller dictionary, therebyobtaining a much faster compression time, but at the possible cost of alower compression ratio. The desired performance of a compressionalgorithm and the system in which the data compression is employed, willvary depending on the application.

Thus, one challenge in employing data compression for a givenapplication or system is selecting one or more optimal compressionalgorithms from the variety of available algorithms. Indeed, the desiredbalance between speed and efficiency is typically a significant factorthat is considered in determining which algorithm to employ for a givenset of data. Algorithms that compress particularly well usually takelonger to execute whereas algorithms that execute quickly usually do notcompress particularly well.

Accordingly, a system and method that would provide dynamic modificationof compression system parameters so as to provide an optimal balancebetween execution speed of the algorithm (compression rate) and theresulting compression ratio, is highly desirable.

Yet another problem within the current art is data storage and retrievalbandwidth limitations. Modern computers utilize a hierarchy of memorydevices. In order to achieve maximum performance levels, modernprocessors utilize onboard memory and on board cache to obtain highbandwidth access to both program and data. Limitations in processtechnologies currently prohibit placing a sufficient quantity of onboardmemory for most applications. Thus, in order to offer sufficient memoryfor the operating system(s), application programs, and user data,computers often use various forms of popular off-processor high speedmemory including static random access memory (SRAM), synchronous dynamicrandom access memory (SDRAM), synchronous burst static ram (SBSRAM). Dueto the prohibitive cost of the high-speed random access memory, coupledwith their power volatility, a third lower level of the hierarchy existsfor non-volatile mass storage devices. While mass storage devices offerincreased capacity and fairly economical data storage, their datastorage and retrieval bandwidth is often much less in relation to theother elements of a computing system.

Computers systems represent information in a variety of manners.Discrete information such as text and numbers are easily represented indigital data. This type of data representation is known as symbolicdigital data. Symbolic digital data is thus an absolute representationof data such as a letter, figure, character, mark, machine code, ordrawing.

Continuous information such as speech, music, audio, images and video,frequently exists in the natural world as analog information. As is wellknown to those skilled in the art, recent advances in very large scaleintegration (VLSI) digital computer technology have enabled bothdiscrete and analog information to be represented with digital data.Continuous information represented as digital data is often referred toas diffuse data. Diffuse digital data is thus a representation of datathat is of low information density and is typically not easilyrecognizable to humans in its native form.

Modern computers utilize digital data representation because of itsinherent advantages. For example, digital data is more readilyprocessed, stored, and transmitted due to its inherently high noiseimmunity. In addition, the inclusion of redundancy in digital datarepresentation enables error detection and/or correction. Errordetection and/or correction capabilities are dependent upon the amountand type of data redundancy, available error detection and correctionprocessing, and extent of data corruption.

One outcome of digital data representation is the continuing need forincreased capacity in data processing, storage, and transmittal. This isespecially true for diffuse data where increases in fidelity andresolution create exponentially greater quantities of data. Datacompression is widely used to reduce the amount of data required toprocess, transmit, or store a given quantity of information. In general,there are two types of data compression techniques that may be utilizedeither separately or jointly to encode/decode data: lossless and lossydata compression.

Over the last decade, computer processor performance has improved by atleast a factor of 50. During this same period, magnetic disk storage hasonly improved by a factor of 5. Thus one additional problem with theexisting art is that memory storage devices severely limit theperformance of consumer, entertainment, office, workstation, servers,and mainframe computers for all disk and memory intensive operations.

For example, magnetic disk mass storage devices currently employed in avariety of home, business, and scientific computing applications sufferfrom significant seek-time access delays along with profound read/writedata rate limitations. Currently the fastest available (15,000) rpm diskdrives support only a 40.0 Megabyte per second data rate (MB/sec). Thisis in stark contrast to the modern Personal Computer's PeripheralComponent Interconnect (PCI) Bus's input/output capability of 512 MB/secand internal local bus capability of 1600 MB/sec.

Another problem within the current art is that emergent high performancedisk interface standards such as the Small Computer Systems Interface(SCSI-3), iSCSI, Fibre Channel, AT Attachment UltraDMA/100+, SerialStorage Architecture, and Universal Serial Bus offer only higher datatransfer rates through intermediate data buffering in random accessmemory. These interconnect strategies do not address the fundamentalproblem that all modern magnetic disk storage devices for the personalcomputer marketplace are still limited by the same typical physicalmedia restriction. In practice, faster disk access data rates are onlyachieved by the high cost solution of simultaneously accessing multipledisk drives with a technique known within the art as data striping andredundant array of independent disks (RAID).

RAID systems often afford the user the benefit of increased databandwidth for data storage and retrieval. By simultaneously accessingtwo or more disk drives, data bandwidth may be increased at a maximumrate that is linear and directly proportional to the number of disksemployed. Thus another problem with modern data storage systemsutilizing RAID systems is that a linear increase in data bandwidthrequires a proportional number of added disk storage devices.

Another problem with most modern mass storage devices is their inherentunreliability. Many modern mass storage devices utilize rotatingassemblies and other types of electromechanical components that possessfailure rates one or more orders of magnitude higher than equivalentsolid state devices. RAID systems employ data redundancy distributedacross multiple disks to enhance data storage and retrieval reliability.In the simplest case, data may be explicitly repeated on multiple placeson a single disk drive, on multiple places on two or more independentdisk drives. More complex techniques are also employed that supportvarious trade-offs between data bandwidth and data reliability.

Standard types of RAID systems currently available include RAID Levels0, 1, and 5. The configuration selected depends on the goals to beachieved. Specifically data reliability, data validation, datastorage/retrieval bandwidth, and cost all play a role in defining theappropriate RAID data storage solution. RAID level 0 entails pure datastriping across multiple disk drives. This increases data bandwidth atbest linearly with the number of disk drives utilized. Data reliabilityand validation capability are decreased. A failure of a single driveresults in a complete loss of all data. Thus another problem with RAIDsystems is that low cost improved bandwidth requires a significantdecrease in reliability.

RAID Level 1 utilizes disk mirroring where data is duplicated on anindependent disk subsystem. Validation of data amongst the twoindependent drives is possible if the data is simultaneously accessed onboth disks and subsequently compared. This tends to decrease databandwidth from even that of a single comparable disk drive. In systemsthat offer hot swap capability, the failed drive is removed and areplacement drive is inserted. The data on the failed drive is thencopied in the background while the entire system continues to operate ina performance degraded but fully operational mode. Once the data rebuildis complete, normal operation resumes. Hence, another problem with RAIDsystems is the high cost of increased reliability and associateddecrease in performance.

RAID Level 5 employs disk data striping and parity error detection toincrease both data bandwidth and reliability simultaneously. A minimumof three disk drives is required for this technique. In the event of asingle disk drive failure, that drive may be rebuilt from parity andother data encoded on disk remaining disk drives. In systems that offerhot swap capability, the failed drive is removed and a replacement driveis inserted. The data on the failed drive is then rebuilt in thebackground while the entire system continues to operate in a performancedegraded but fully operational mode. Once the data rebuild is complete,normal operation resumes.

Thus another problem with redundant modern mass storage devices is thedegradation of data bandwidth when a storage device fails. Additionalproblems with bandwidth limitations and reliability similarly occurwithin the art by all other forms of sequential, pseudo-random, andrandom access mass storage devices. Typically mass storage devicesinclude magnetic and optical tape, magnetic and optical disks, andvarious solid-state mass storage devices. It should be noted that thepresent invention applies to all forms and manners of memory devicesincluding storage devices utilizing magnetic, optical, neural andchemical techniques or any combination thereof.

Yet another problem within the current art is the application and use ofvarious data compression techniques. It is well known within the currentart that data compression provides several unique benefits. First, datacompression can reduce the time to transmit data by more efficientlyutilizing low bandwidth data links. Second, data compression economizeson data storage and allows more information to be stored for a fixedmemory size by representing information more efficiently.

For purposes of discussion, data compression is canonically divided intolossy and lossless techniques. Lossy data compression techniques providefor an inexact representation of the original uncompressed data suchthat the decoded (or reconstructed) data differs from the originalunencoded/uncompressed data. Lossy data compression is also known asirreversible or noisy compression. Negentropy is defined as the quantityof information in a given set of data. Thus, one obvious advantage oflossy data compression is that the compression ratios can be larger thanthat dictated by the negentropy limit, all at the expense of informationcontent. Many lossy data compression techniques seek to exploit varioustraits within the human senses to eliminate otherwise imperceptibledata. For example, lossy data compression of visual imagery might seekto delete information content in excess of the display resolution orcontrast ratio of the target display device.

On the other hand, lossless data compression techniques provide an exactrepresentation of the original uncompressed data. Simply stated, thedecoded (or reconstructed) data is identical to the originalunencoded/uncompressed data. Lossless data compression is also known asreversible or noiseless compression. Thus, lossless data compressionhas, as its current limit, a minimum representation defined by theentropy of a given data set.

A rich and highly diverse set of lossless data compression anddecompression algorithms exist within the current art. These range fromthe simplest “adhoc” approaches to highly sophisticated formalizedtechniques that span the sciences of information theory, statistics, andartificial intelligence. One fundamental problem with almost all modernapproaches is the compression ratio to encoding and decoding speedachieved. As previously stated, the current theoretical limit for datacompression is the entropy limit of the data set to be encoded. However,in practice, many factors actually limit the compression ratio achieved.Most modern compression algorithms are highly content dependent. Contentdependency exceeds the actual statistics of individual elements andoften includes a variety of other factors including their spatiallocation within the data set.

Of popular compression techniques, arithmetic coding possesses thehighest degree of algorithmic effectiveness, and as expected, is theslowest to execute. This is followed in turn by dictionary compression,Huffman coding, and run-length coding with respectively decreasingexecute times. What is not apparent from these algorithms, that is alsoone major deficiency within the current art, is knowledge of theiralgorithmic efficiency. More specifically, given a compression ratiothat is within the effectiveness of multiple algorithms, the questionarises as their corresponding efficiency.

Within the current art there also presently exists a strong inverserelationship between achieving the maximum (current) theoreticalcompression ratio, which we define as algorithmic effectiveness, andrequisite processing time. For a given single algorithm theeffectiveness over a broad class of data sets including text, graphics,databases, and executable object code is highly dependent upon theprocessing effort applied. Given a baseline data set, processoroperating speed and target architecture, along with its associatedsupporting memory and peripheral set, we define algorithmic efficiencyas the time required to achieve a given compression ratio. Algorithmicefficiency assumes that a given algorithm is implemented in an optimumobject code representation executing from the optimum places in memory.This is almost never achieved in practice due to limitations withinmodern optimizing software compilers. It should be further noted that anoptimum algorithmic implementation for a given input data set may not beoptimum for a different data set. Much work remains in developing acomprehensive set of metrics for measuring data compression algorithmicperformance, however for present purposes the previously defined termsof algorithmic effectiveness and efficiency should suffice.

Various solutions to this problem of optimizing algorithmicimplementation are found in U.S. Pat. Nos. 6,195,024 and 6,309,424,issued on Feb. 27, 2001 and Oct. 30, 2001, respectively, to JamesFallon, both of which are entitled “Content Independent Data CompressionMethod and System,” and are incorporated herein by reference. Thesepatents describe data compression methods that providecontent-independent data compression, wherein an optimal compressionratio for an encoded stream can be achieved regardless of the datacontent of the input data stream. As more fully described in the aboveincorporated patents, a data compression protocol comprises applying aninput data stream to each of a plurality of different encoders to, ineffect, generate a plurality of encoded data streams. The plurality ofencoders are preferably selected based on their ability to effectivelyencode different types of input data. The final compressed data streamis generated by selectively combining blocks of the compressed streamsoutput from the plurality of encoders based on one or more factors suchas the optimal compression ratios obtained by the plurality of decoders.The resulting compressed output stream can achieve the greatest possiblecompression, preferably in real-time, regardless of the data content.

Yet another problem within the current art relates to data managementand the use of existing file management systems. Present computeroperating systems utilize file management systems to store and retrieveinformation in a uniform, easily identifiable, format. Files arecollections of executable programs and/or various data objects. Filesoccur in a wide variety of lengths and must be stored within a datastorage device. Most storage devices, and in particular, mass storagedevices, work most efficiently with specific quantities of data. Forexample, modern magnetic disks are often divided into cylinders, headsand sectors. This breakout arises from legacy electro-mechanicalconsiderations with the format of an individual sector often some binarymultiple of bytes (512, 1024, . . . ). A fixed or variable quantity ofsectors housed on an individual track. The number of sectors permittedon a single track is limited by the number of reliable flux reversalsthat can be encoded on the storage media per linear inch, often referredto as linear bit density. In disk drives with multiple heads and diskmedia, a single cylinder is comprised of multiple tracks.

A file allocation table is often used to organize both used and unusedspace on a mass storage device. Since a file often comprises more thanone sector of data, and individual sectors or contiguous strings ofsectors may be widely dispersed over multiple tracks and cylinders, afile allocation table provides a methodology of retrieving a file orportion thereof. File allocation tables are usually comprised of stringsof pointers or indices that identify where various portions of a fileare stored.

In-order to provide greater flexibility in the management of diskstorage at the media side of the interface, logical block addresses havebeen substituted for legacy cylinder, head, sector addressing. Thispermits the individual disk to optimize its mapping from the logicaladdress space to the physical sectors on the disk drive. Advantages withthis technique include faster disk accesses by allowing the diskmanufacturer greater flexibility in managing data interleaves and otherhigh-speed access techniques. In addition, the replacement of bad mediasectors can take place at the physical level and need not be the concernof the file allocation table or host computer. Furthermore, these badsector replacement maps are definable on a disk by disk basis.

Practical limitations in the size of the data required to both representand process an individual data block address, along with the size ofindividual data blocks, governs the type of file allocation tablescurrently in use. For example, a 4096 byte logical block size (8sectors) employed with 32 bit logical block addresses. This yields anaddressable data space of 17.59 Terabytes. Smaller logical blocks permitmore efficient use of disk space. Larger logical blocks support a largeraddressable data space. Thus one limitation within the current art isthat disk file allocation tables and associated file management systemsare a compromise between efficient data storage, access speed, andaddressable data space.

Data in a computer has various levels of information content. Evenwithin a single file, many data types and formats are utilized. Eachdata representation has specific meaning and each may hold differingquantities of information. Within the current art, computers processdata in a native, uncompressed, format. Thus compressed data must oftenbe decompressed prior to performing various data processing functions oroperations. Modern file systems have been designed to work with data inits native format. Thus another significant problem within the currentart is that file systems are not able to randomly access compressed datain an efficient manner.

Further aggravating this problem is the fact that when data isdecompressed, processed and recompressed it may not fit back into itsoriginal disk space, causing disk fragmentation or complex disk spacereallocation requirements. Several solutions exist within the currentart including file by file and block structured compressed datamanagement.

In file by file compression, each file is compressed when stored on diskand decompressed when retrieved. For very small files this technique isoften adequate, however for larger files the compression anddecompression times are too slow, resulting in inadequate system levelperformance. In addition, the ability to access randomly access datawithin a specific file is lost. The one advantage to file by filecompression techniques is that they are easy to develop and arecompatible with existing file systems. Thus file by file compressed datamanagement is not an adequate solution.

Block structured disk compression operates by compressing anddecompressing fixed block sizes of data. Block sizes are often fixed,but may be variable in size. A single file usually is comprised ofmultiple blocks, however a file may be so small as to fit within asingle block. Blocks are grouped together and stored in one or more disksectors as a group of Blocks (GOBs). A group of blocks is compressed anddecompressed as a unit, thus there exists practical limitations on thesize of GOBs. Most compression algorithms achieve a higher level ofalgorithmic effectiveness when operating on larger quantities of data.Restated, the larger the quantity of data processed with a uniforminformation density, the higher the compressions ratio achieved. If GOBsare small compression ratios are low and processing time short.Conversely, when GOBS are large compression ratios are higher andprocessing time is longer. Large GOBs tend to perform in a manneranalogous to file by file compression. The two obvious benefits to blockstructured disk compression are psuedo-random data access and reduceddata compression/decompression processing time.

Several problems exist within the current art for the management ofcompressed blocks. One method for storage of compressed files on disk isby contiguously storing all GOBs corresponding to a single file. Howeveras files are processed within the computers, files may grow or shrink insize. Inefficient disk storage results when a substantial file sizereduction occurs. Conversely when a file grows substantially, theadditional space required to store the data may not be availablecontiguously. The result of this process is substantial diskfragmentation and slower access times.

An alternate method is to map compressed GOBs into the next logical freespace on the disk. One problem with this method is that average fileaccess times are substantially increased by this technique due to therandom data storage. Peak access delays may be reduced since thestatistics behave with a more uniform white spectral density, howeverthis is not guaranteed.

A further layer of complexity is encountered when compressed informationis to be managed on more than one data storage device. Competingrequirements of data access bandwidth, data reliability/redundancy, andefficiency of storage space are encountered.

These and other limitations within the current art are solved with thepresent invention.

SUMMARY OF THE INVENTION

The present invention is directed to a system and method for compressingand decompressing based on the actual or expected throughput (bandwidth)of a system employing data compression and a technique of optimizingbased upon planned, expected, predicted, or actual usage.

In one aspect of the present invention, a system for providing bandwidthsensitive data compression comprises:

a data compression system for compressing and decompressing data inputto the system;

a plurality of compression routines selectively utilized by the datacompression system; and

a controller for tracking the throughput of the system and generating acontrol signal to select a compression routine based on the systemthroughput. In a preferred embodiment, when the controller determinesthat the system throughput falls below a predetermined throughputthreshold, the controller commands the data compression engine to use acompression routine providing a faster rate of compression so as toincrease the throughput.

In another aspect, a system for providing bandwidth sensitive datacompression comprises a plurality of access profiles, operativelyaccessible by the controller that enables the controller to determine acompression routine that is associated with a data type of the data tobe compressed. The access profiles comprise information that enables thecontroller to select a suitable compression algorithm that provides adesired balance between execution speed (rate of compression) andefficiency (compression ratio).

In yet another aspect, a system comprises a data storage controller forcontrolling the compression and storage of compressed data to a storagedevice and the retrieval and decompression of compressed data from thestorage device. The system throughput tracked by the controllerpreferably comprises a number of pending access requests to a storagedevice.

In another aspect, the system comprises a data transmission controllerfor controlling the compression and transmission of compressed data, aswell as the decompression of compressed data received over acommunication channel. The system throughput tracked by the controllercomprises a number of pending transmission requests over thecommunication channel.

In yet another aspect of the present invention, a method for providingbandwidth sensitive data compression in a data processing system,comprises the steps of:

compressing data using an first compression routine providing a firstcompression rate;

tracking the throughput of the data processing system to determine ifthe first compression rate provides a throughput that meets apredetermined throughput threshold; and

compressing data using a second compression routine providing a secondcompression rate that is greater than the first compression rate, if thetracked throughput does not meet the predetermined throughput threshold.

Preferably, the first compression routine comprises a default asymmetricroutine and wherein the second compression routine comprises a symmetricroutine.

In another aspect, the method comprises processing a user command toload a user-selected compression routine for compressing data.

In another aspect, the method further comprises processing a usercommand to compress user-provided data and automatically selecting acompression routine associated with a data type of the user-provideddata.

These and other aspects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a high-level block diagram of a system for providing bandwidthsensitive data compression/decompression according to an embodiment ofthe present invention.

FIG. 2 is a flow diagram of a method for providing bandwidth sensitivedata compression/decompression according to one aspect of the presentinvention.

FIG. 3 is a block diagram of a preferred system for implementing abandwidth sensitive data compression/decompression method according toan embodiment of the present invention.

FIG. 4 a is a diagram of a file system format of a virtual and/orphysical disk according to an embodiment of the present invention.

FIG. 4 b is a diagram of a data structure of a sector map entry of avirtual block table according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to a system and method for compressingand decompressing based on the actual or expected throughput (bandwidth)of a system employing data compression. Although one of ordinary skillin the art could readily envision various implementations for thepresent invention, a preferred system in which this invention isemployed comprises a data storage controller that preferably utilizes areal-time data compression system to provide “accelerated” data storageand retrieval bandwidths. The concept of “accelerated” data storage andretrieval was introduced in co-pending U.S. patent application Ser. No.09/266,394, filed Mar. 11, 1999, entitled “System and Methods ForAccelerated Data Storage and Retrieval” and co-pending U.S. patentapplication Ser. No. 09/481,243, filed Jan. 11, 2000, entitled “Systemand Methods For Accelerated Data Storage and Retrieval,” both of whichare commonly assigned and incorporated herein by reference.

In general, as described in the above-incorporated applications,“accelerated” data storage comprises receiving a digital data stream ata data transmission rate which is greater than the data storage rate ofa target storage device, compressing the input stream at a compressionrate that increases the effective data storage rate of the targetstorage device and storing the compressed data in the target storagedevice. For instance, assume that a mass storage device (such as a harddisk) has a data storage rate of 20 megabytes per second. If a storagecontroller for the mass storage device is capable of compressing (inreal time) an input data stream with an average compression rate of 3:1,then data can be stored in the mass storage device at a rate of 60megabytes per second, thereby effectively increasing the storagebandwidth (“storewidth”) of the mass storage device by a factor ofthree. Similarly, accelerated data retrieval comprises retrieving acompressed digital data stream from a target storage device at the rateequal to, e.g., the data access rate of the target storage device andthen decompressing the compressed data at a rate that increases theeffective data access rate of the target storage device. Advantageously,providing accelerated data storage and retrieval at (or close to)real-time can reduce or eliminate traditional bottlenecks associatedwith, e.g., local and network disk accesses.

In a preferred embodiment, the present invention is implemented forproviding accelerated data storage and retrieval. In one embodiment, acontroller tracks and monitors the throughput (data storage andretrieval) of a data compression system and generates control signals toenable/disable different compression algorithms when, e.g., a bottleneckoccurs so as to increase the throughput and eliminate the bottleneck.

In the following description of preferred embodiments, two categories ofcompression algorithms are defined—an “asymmetrical” data compressionalgorithm and a “symmetrical data compression algorithms. Anasymmetrical data compression algorithm is referred to herein as one inwhich the execution time for the compression and decompression routinesdiffer significantly. In particular, with an asymmetrical algorithm,either the compression routine is slow and the decompression routine isfast or the compression routine is fast and the decompression routine isslow. Examples of asymmetrical compression algorithms includedictionary-based compression schemes such as Lempel-Ziv.

On the other hand, a “symmetrical” data compression algorithm isreferred to herein as one in which the execution time for thecompression and the decompression routines are substantially similar.Examples of symmetrical algorithms include table-based compressionschemes such as Huffman. For asymmetrical algorithms, the totalexecution time to perform one compress and one decompress of a data setis typically greater than the total execution time of symmetricalalgorithms. But an asymmetrical algorithm typically achieves highercompression ratios than a symmetrical algorithm.

It is to be appreciated that in accordance with the present invention,symmetry may be defined in terms of overall effective bandwidth,compression ratio, or time or any combination thereof. In particular, ininstances of frequent data read/writes, bandwidth is the optimalparameter for symmetry. In asymmetric applications such as operatingsystems and programs, the governing factor is net decompressionbandwidth, which is a function of both compression speed, which governsdata retrieval time, and decompression speed, wherein the total governsthe net effective data read bandwidth. These factors work in ananalogous manner for data storage where the governing factors are bothcompression ratio (storage time) and compression speed. The presentinvention applies to any combination or subset thereof, which isutilized to optimize overall bandwidth, storage space, or any operatingpoint in between.

Referring now to FIG. 1, a high-level block diagram illustrates a systemfor providing bandwidth sensitive data compression/decompressionaccording to an embodiment of the present invention. In particular, FIG.1 depicts a host system 10 comprising a controller 11 (e.g., a filemanagement system), a compression/decompression system 12, a pluralityof compression algorithms 13, a storage medium 14, and a plurality ofdata profiles 15. The controller tracks and monitors the throughput(e.g., data storage and retrieval) of the data compression system 12 andgenerates control signals to enable/disable different compressionalgorithms 13 when the throughput falls below a predetermined threshold.In one embodiment, the system throughput that is tracked by thecontroller 11 preferably comprises a number of pending access requeststo the memory system.

The compression system 12 is operatively connected to the storage medium14 using suitable protocols to write and read compressed data to andfrom the storage medium 14. It is to be understood that the storagemedium 14 may comprise any form of memory device including all forms ofsequential, pseudo-random, and random access storage devices. The memorystorage device 14 may be volatile or non-volatile in nature, or anycombination thereof. Storage devices as known within the current artinclude all forms of random access memory, magnetic and optical tape,magnetic and optical disks, along with various other forms ofsolid-state mass storage devices. Thus it should be noted that thecurrent invention applies to all forms and manners of memory devicesincluding, but not limited to, storage devices utilizing magnetic,optical, and chemical techniques, or any combination thereof. The datacompression system 12 preferably operates in real-time (or substantiallyreal-time) to compress data to be stored on the storage device 14 and todecompress data that is retrieved from the storage device 14. Inaddition, the compression system 12 may receive data (compressed or notcompressed) via an I/O (input/output) port 16 that is transmitted over atransmission line or communication channel from a remote location, andthen process such data (e.g., decompress or compress the data). Thecompression system 12 may further transmit data (compressed ordecompressed) via the I/O port 16 to another network device for remoteprocessing or storage.

The controller 11 utilizes information comprising a plurality of dataprofiles 15 to determine which compression algorithms 13 should be usedby the compression system 12. In a preferred embodiment, the compressionalgorithms 13 comprise one or more asymmetric algorithms. As notedabove, with asymmetric algorithms, the compression ratio is typicallygreater than the compression ratios obtained using symmetricalalgorithms. Preferably, a plurality of asymmetric algorithms areselected to provide one or more asymmetric algorithms comprising a slowcompress and fast decompress routine, as well as one or more asymmetricalgorithms comprising a fast compress and slow decompress routine.

The compression algorithms 14 further comprise one or more symmetricalgorithms, each having a compression rate and correspondingdecompression rate that is substantially equal. Preferably, a pluralityof symmetric algorithms are selected to provide a desired range ofcompression and decompression rates for data to be processed by asymmetric algorithm.

In a preferred embodiment, the overall throughput (bandwidth) of thesystem 10 is one factor considered by the controller 11 in decidingwhether to use an asymmetrical or symmetrical compression algorithm forprocessing data stored to, and retrieved from, the storage device 14.Another factor that is used to determine the compression algorithm isthe type of data to be processed. In a preferred embodiment, the dataprofiles 15 comprise information regarding predetermined access profilesof different data sets, which enables the controller 11 to select asuitable compression algorithm based on the data type. For instance, thedata profiles may comprise a map that associates different data types(based on, e.g., a file extension) with preferred one(s) of thecompression algorithms 13. For example, preferred access profilesconsidered by the controller 11 are set forth in the following table.

Access Profile 1: Access Profile 2 Access Profile 3 Data is written to aData is written The amount of times data storage medium once to thestorage is read from and written (or very few times) medium often to thestorage medium is but is read from the but read few substantially thesame. storage medium many times times

With Access Profile 1, the decompression routine would be executedsignificantly more times than the corresponding compression routine.This is typical with operating systems, applications and websites, forexample. Indeed, an asymmetrical application can be used to (offline)compress an (OS) operating system, application or Website using a slowcompression routine to achieve a high compression ratio. After thecompressed OS, application or website is stored, the asymmetricalgorithm is then used during runtime to decompress, at a significantrate, the OS, application or website launched or accessed by a user.

Therefore, with data sets falling within Access Profile 1, it ispreferable to utilize an asymmetrical algorithm that provides a slowcompression routine and a fast decompression routine so as to provide anincrease in the overall system performance as compared the performancethat would be obtained using a symmetrical algorithm. Further, thecompression ratio obtained using the asymmetrical algorithm would likelybe higher than that obtained using a symmetrical algorithm (thuseffectively increasing the storage capacity of the storage device).

With Access Profile 2, the compression routine would be executedsignificantly more times than the decompression routine. This is typicalwith a system for automatically updating an inventory database, forexample, wherein an asymmetric algorithm that provides a fastcompression routine and a slow decompression routine would provide anoverall faster (higher throughput) and efficient (higher compressionratio) system performance than would be obtained using a symmetricalalgorithm.

With Access Profile 3, where data is accessed with a similar number ofreads and writes, the compression routine would be executedapproximately the same number of times as the decompression routine.This is typical of most user-generated data such as documents andspreadsheets. Therefore, it is preferable to utilize a symmetricalalgorithm that provides a relatively fast compression and decompressionroutine. This would result in an overall system performance that wouldbe faster as compared to using an asymmetrical algorithm (although thecompression ratio achieved may be lower).

The following table summarizes the three data access profiles and thetype of compression algorithm that would produce optimum throughput.

Example Data Compression Compressed Data Decompression Access ProfileTypes Algorithm Characteristics Algorithm 1. Write OperatingAsymmetrical Very high Asymmetrical few, Read systems, (Slow compression(Fast many Programs, Web compress) ratio decompress) sites 2. WriteAutomatically Asymmetrical Very high Asymmetrical many, updated (Fastcompression (Slow Read few inventory compress) ratio decompress)database 3. Similar User generated Symmetrical Standard Symmetricalnumber of documents compression Reads and Writes ratio

In accordance with the present invention, the access profile of a givendata set is known a priori or determined prior to compression so thatthe optimum category of compression algorithm can be selected. Asexplained below, the selection process may be performed either manuallyor automatically by the controller 11 of the data compression system 12.Further, the decision regarding which routines will be used atcompression time (write) and at decompression time (read) is preferablymade before or at the time of compression. This is because once data iscompressed using a certain algorithm, only the matching decompressionroutine can be used to decompress the data, regardless of how muchprocessing time is available at the time of decompression.

Referring now to FIG. 2, a flow diagram illustrates a method forproviding bandwidth sensitive data compression according to one aspectof the present invention. For purposes of illustration, it is assumedthat the method depicted in FIG. 2 is implemented with a disk controllerfor providing accelerated data storage and retrieval from a hard disk ona PC (personal computer). The data compression system is initializedduring a boot-up process after the PC is powered-on and a defaultcompression/decompression routine is instantiated (step 20).

In a preferred embodiment, the default algorithm comprises anasymmetrical algorithm since an operating system and applicationprograms will be read from hard disk memory and decompressed during theinitial use of the system 10. Indeed, as discussed above, an asymmetricalgorithm that provides slow compression and fast decompression ispreferable for compressing operating systems and applications so as toobtain a high compression ratio (to effectively increase the storagecapacity of the hard disk) and fast data access (to effectively increasethe retrieval rate from the hard disk). The initial asymmetric routinethat is applied (by, e.g., a vendor) to compress the operating systemand applications is preferably set as the default. The operating systemwill be retrieved and then decompressed using the default asymmetricroutine (step 21).

During initial runtime, the controller will maintain use the defaultalgorithm until certain conditions are met. For instance, if a readcommand is received (affirmative result in step 22), the controller willdetermine whether the data to be read from disk can be compressed usingthe current routine (step 23). For this determination, the controllercould, e.g., read a flag value that indicates the algorithm that wasused to compress the file. If the data can be decompressed using thecurrent algorithm (affirmative determination in step 23), then the filewill be retrieved and decompressed (step 25). On the other hand, if thedata cannot be decompressed using the current algorithm (negativedetermination in step 23), the controller will issue the appropriatecontrol signal to the compression system to load the algorithmassociated with the file (step 24) and, subsequently, decompress thefile (step 25).

If a write command is received (affirmative result in step 26), the datato be stored will be compressed using the current algorithm (step 27).During the process of compression and storing the compressed data, thecontroller will track the throughput to determine whether the throughputis meeting a predetermined threshold (step 28). For example, thecontroller may track the number of pending disk accesses (accessrequests) to determine whether a bottleneck is occurring. If thethroughput of the system is not meeting the desired threshold (e.g., thecompression system cannot maintain the required or requested data rates)(negative determination in step 28), then the controller will commandthe data compression system to utilize a compression routine providingfaster compression (e.g., a fast symmetric compression algorithm) (step29) so as to mitigate or eliminate the bottleneck.

If, on the other hand, the system throughput is meeting or exceeding thethreshold (affirmative determination in step 28) and the currentalgorithm being used is a symmetrical routine (affirmative determinationin step 30), in an effort to achieve optimal compression ratios, thecontroller will command the data compression system to use an asymmetriccompression algorithm (step 31) that may provide a slower rate ofcompression, but provide efficient compression.

This process is repeated such that whenever the controller determinesthat the compression system can maintain the required/requested datathroughput using a slow (highly efficient) asymmetrical compressionalgorithm, the controller will allow the compression system to operatein the asymmetrical mode. This will allow the system to obtain maximumstorage capacity on the disk. Further, the controller will command thecompression system to use a symmetric routine comprising a fastcompression routine when the desired throughput is not met. This willallow the system to, e.g., service the backlogged disk accesses. Then,when the controller determines that the required/requested data ratesare subsequently lower and the compression system can maintain the datarate, the controller can command the compression system to use a slower(but more efficient) asymmetric compression algorithm.

With the above-described method depicted in FIG. 2, the selection of thecompression routine is performed automatically by the controller so asto optimize system throughput. In another embodiment, a user thatdesires to install a program or text files, for example, can command thesystem (via a software utility) to utilize a desired compression routinefor compressing and storing the compressed program or files to disk. Forexample, for a power user, a GUI menu can be displayed that allows theuser to directly select a given algorithm. Alternatively, the system candetect the type of data being installed or stored to disk (via fileextension, etc.) and automatically select an appropriate algorithm usingthe Access Profile information as described above. For instance, theuser could indicate to the controller that the data being installedcomprises an application program which the controller would determinefalls under Access Profile 1. The controller would then command thecompression engine to utilize an asymmetric compression algorithmemploying a slow compression routine and a fast decompression routine.The result would be a one-time penalty during program installation (slowcompression), but with fast access to the data on all subsequentexecutions (reads) of the program, as well as a high compression ratio.

It is to be appreciated that the present invention may be implemented inany data processing system, device, or apparatus using data compression.For instance, the present invention may be employed in a datatransmission controller in a network environment to provide accelerateddata transmission over a communication channel (i.e., effectivelyincrease the transmission bandwidth by compressing the data at thesource and decompressing data at the receiver, in real-time).

Further, the present invention can be implemented with a data storagecontroller utilizing data compression and decompression to providedaccelerated data storage and retrieval from a mass storage device.Exemplary embodiments of preferred data storage controllers in which thepresent invention may be implemented are described, for example, in U.S.patent application Ser. No. 09/775,905, filed on Feb. 2, 2001, entitled“Data Storewidth Accelerator”, which is commonly assigned and fullyincorporated herein by reference.

FIG. 3 illustrates a preferred embodiment of a data storage controller120 as described in the above-incorporated U.S. Ser. No. 09/775,905 forimplementing a bandwidth sensitive data compression protocol asdescribed herein. The storage controller 120 comprises a DSP (digitalsignal processor) 121 (or any other micro-processor device) thatimplements a data compression/decompression routine. The DSP 121preferably employs a plurality of symmetric and asymmetriccompression/decompression as described herein. The data storagecontroller 120 further comprises at least one programmable logic device122 (or volatile logic device). The programmable logic device 122preferably implements the logic (program code) for instantiating anddriving both a disk interface 114 and a bus interface 115 and forproviding full DMA (direct memory access) capability for the disk andbus interfaces 114, 115. Further, upon host computer power-up and/orassertion of a system-level “reset” (e.g., PCI Bus reset), the DSP 121initializes and programs the programmable logic device 122 before of thecompletion of initialization of the host computer. This advantageouslyallows the data storage controller 120 to be ready to accept and processcommands from the host computer (via the bus 116) and retrieve boot datafrom the disk (assuming the data storage controller 120 is implementedas the boot device and the hard disk stores the boot data (e.g.,operating system, etc.))

The data storage controller 120 further comprises a plurality of memorydevices including a RAM (random access memory) device 123 and a ROM(read only memory) device 124 (or FLASH memory or other types ofnon-volatile memory). The RAM device 123 is utilized as on-board cacheand is preferably implemented as SDRAM. The ROM device 124 is utilizedfor non-volatile storage of logic code associated with the DSP 121 andconfiguration data used by the DSP 121 to program the programmable logicdevice 122.

The DSP 121 is operatively connected to the memory devices 123, 124 andthe programmable logic device 122 via a local bus 125. The DSP 121 isalso operatively connected to the programmable logic device 122 via anindependent control bus 126. The programmable logic device 122 providesdata flow control between the DSP 121 and the host computer systemattached to the bus 116, as well as data flow control between the DSP121 and the storage device. A plurality of external I/O ports 127 areincluded for data transmission and/or loading of one or moreprogrammable logic devices. Preferably, the disk interface 114 driven bythe programmable logic device 122 supports a plurality of hard drives.

The storage controller 120 further comprises computer reset and power upcircuitry 128 (or “boot configuration circuit”) for controllinginitialization (either cold or warm boots) of the host computer systemand storage controller 120. A preferred boot configuration circuit andpreferred computer initialization systems and protocols are described inU.S. patent application Ser. No. 09/775,897, filed on Feb. 2, 2001,entitled “System and Methods For Computer Initialization,” which iscommonly assigned and incorporated herein by reference. Preferably, theboot configuration circuit 128 is employed for controlling theinitializing and programming the programmable logic device 122 duringconfiguration of the host computer system (i.e., while the CPU of thehost is held in reset). The boot configuration circuit 128 ensures thatthe programmable logic device 122 (and possibly other volatile orpartially volatile logic devices) is initialized and programmed beforethe bus 116 (such as a PCI bus) is fully reset. In particular, whenpower is first applied to the boot configuration circuit 128, the bootconfiguration circuit 28 generates a control signal to reset the localsystem (e.g., storage controller 120) devices such as a DSP, memory, andI/O interfaces. Once the local system is powered-up and reset, thecontrolling device (such as the DSP 121) will then proceed toautomatically determine the system environment and configure the localsystem to work within that environment. By way of example, the DSP 121of the disk storage controller 120 would sense that the data storagecontroller 120 is on a PCI computer bus (expansion bus) and has attachedto it a hard disk on an IDE interface. The DSP 121 would then load theappropriate PCI and IDE interfaces into the programmable logic device122 prior to completion of the host system reset. Once the programmablelogic device 122 is configured for its environment, the boot devicecontroller is reset and ready to accept commands over thecomputer/expansion bus 116.

It is to be understood that the data storage controller 120 may beutilized as a controller for transmitting data (compressed oruncompressed) to and from remote locations over the DSP I/O ports 127 orsystem bus 116, for example. Indeed, the I/O ports 127 of the DSP 121may be used for transmitting data (compressed or uncompressed) that iseither retrieved from the disk or received from the host system via thebus 116, to remote locations for processing and/or storage. Indeed, theI/O ports may be operatively connected to other data storage controllersor to a network communication channels. Likewise, the data storagecontroller 120 may receive data (compressed or uncompressed) over theI/O ports 127 of the DSP 121 from remote systems that are connected tothe I/O ports 127 of the DSP, for local processing by the data storagecontroller 120. For instance, a remote system may remotely access thedata storage controller 120 (via the I/O ports of the DSP or system bus116) to utilize the data compression, in which case the data storagecontroller 120 would transmit the compressed data back to the systemthat requested compression.

In accordance with the present invention, the system (e.g., data storagecontroller 120) preferably boots-up in a mode using asymmetrical datacompression. It is to be understood that the boot process would not beaffected whether the system boots up defaulting to an asymmetrical modeor to a symmetrical mode. This is because during the boot process of thecomputer, it is reading the operating system from the disk, not writing.However, once data is written to the disk using a compression algorithm,it must retrieve and read the data using the corresponding decompressionalgorithm.

As the user creates, deletes and edits files, the disk controller 120will preferably utilize an asymmetrical compression routine thatprovides slow compression and fast decompression. Since using theasymmetrical compression algorithm will provide slower compression thana symmetrical algorithm, the file system of the computer will trackwhether the disk controller 120 has disk accesses pending. If the diskcontroller 120 does have disk accesses pending and the system isstarting to slow down, the file management system will command the diskcontroller 120 to use a faster symmetrical compression algorithm. Ifthere are no disk access requests pending, the file management systemwill leave the disk controller in the mode of using the asymmetricalcompression algorithm.

If the disk controller 120 was switched to using a symmetricalalgorithm, the file management system will preferably signal thecontroller to switch back to a default asymmetrical algorithm when,e.g., the rate of the disk access requests slow to the point where thereare no pending disk accesses.

At some point a user may decide to install software or load files ontothe hard disk. Before installing the software, for example, as describedabove, the user could indicate to the disk controller 120 (via asoftware utility) to enter and remain in an asymmetric mode using anasymmetric compression algorithm with a slow compression routine and avery fast decompression routine. The disk controller would continue touse the asymmetrical algorithm until commanded otherwise, regardless ofthe number of pending disk accesses. Then, after completing the softwareinstallation, the user would then release the disk controller from this“asymmetrical only” mode of operation (via the software utility).

Again, when the user is not commanding the disk controller 120 to remainin a certain mode, the file management system will determine whether thedisk controller should use the asymmetrical compression algorithms orthe symmetrical compression algorithms based on the amount of backloggeddisk activity. If the backlogged disk activity exceeds a threshold, thenthe file management system will preferably command the disk controllerto use a faster compression algorithm, even though compressionperformance may suffer. Otherwise, the file management system willcommand the disk controller to use the asymmetrical algorithm that willyield greater compression performance.

It is to be appreciated that the data compression methods describedherein by be integrated or otherwise implemented with the contentindependent data compression methods described in the above-incorporatedU.S. Pat. Nos. 6,195,024 and 6,309,424.

In yet another embodiment of the present invention a virtual filemanagement system is utilized to store, retrieve, or transmit compressedand/or accelerated data. In one embodiment of the present invention, aphysical or virtual disk is utilized employing a representative filesystem format as illustrated in FIG. 4. As shown in FIG. 4, a virtualfile system format comprises one or more data items. For instance, a“Superblock” denotes a grouping of configuration information necessaryfor the operation of the disk management system. The Superblocktypically resides in the first sector of the disk. Additional copies ofthe Superblock are preferably maintained on the disk for backuppurposes. The number of copies will depend on the size of the disk. Onesector is preferably allocated for each copy of the Superblock on thedisk, which allows storage to add additional parameters for variousapplications. The Superblock preferably comprises information such as(i) compress size; (ii) virtual block table address; (iii) virtual blocktable size; (iv) allocation size; (v) number of free sectors(approximate); (vi) ID (“Magic”) number; and (vii) checksum

The “compress size” refers to the maximum uncompressed size of data thatis grouped together for compression (referred to as a “data chunk”). Forexample, if the compress size is set to 16 k and a 40 k data block issent to the disk controller for storage, it would be divided into two 16k chunks and one 8 k chunk. Each chunk would be compressed separatelyand possess it's own header. As noted above, for many compressionalgorithms, increasing the compression size will increase thecompression ratio obtained. However, even when a single byte is neededfrom a compressed data chunk, the entire chunk must be decompressed,which is a tradeoff with respect to using a very large compression size.

The “virtual block table address” denotes the physical address of thevirtual block table. The “virtual block table size” denotes the size ofthe virtual block table.

The “allocation size” refers to the minimum number of contiguous sectorson the disk to reserve for each new data entry. For example, assumingthat 4 sectors are allowed for each allocation and that a compresseddata entry requires only 1 sector, then the remaining 3 sectors would beleft unused. Then, if that piece of data were to be appended, therewould be room to increase the data while remaining contiguous on thedisk. Indeed, by maintaining the data contiguously, the speed at whichthe disk can read and write the data will increase. Although thecontroller preferably attempts to keep these unused sectors availablefor expansion of the data, if the disk were to fill up, the controllercould use such sectors to store new data entries. In this way, a systemcan be configured to achieve greater speed, while not sacrificing diskspace. Setting the allocation size to 1 sector would effectively disablethis feature.

The “number Of free sectors” denotes the number of physical free sectorsremaining on the disk. The ID (“Magic) number” identifies this data as aSuperblock. The “checksum” comprises a number that changes based on thedata in the Superblock and is used for error checking. Preferably, thisnumber is chosen so that all of the words in the Superblock (includingthe checksum) added up are equal to zero.

The “virtual block table” (VET) comprises a number of “sector map”entries, one for each grouping of compressed data (or chunks). The VBTmay reside anywhere on the disk. The size of the VBT will depend on howmuch data is on the disk. Each sector map entry comprises 8 bytes.Although there is preferably only one VBT on the disk, each chunk ofcompressed data will have a copy of its sector map entry in its header.If the VET were to become corrupted, scanning the disk for all sectormaps could create a new one.

The term “type” refers to the sector map type. For example, a value of“00” corresponds to this sector map definition. Other values arepreferably reserved for future redefinitions of the sector map.

A “C Type” denotes a compression type. A value of “000” will correspondto no compression. Other values are defined as required depending on theapplication. This function supports the use of multiple compressionalgorithms along with the use of various forms of asymmetric datacompression.

The “C Info” comprises the compression information needed for the givencompression type. These values are defined depending on the application.In addition, the data may be tagged based on it's use—for exampleoperating system “00”, Program “01”, or data “10”. Frequency of use oraccess codes may also be included. The size of this field may be greatlyexpanded to encode statistics supporting these items including, forexample, cumulative number of times accessed, number of times accessedwithin a given time period or CPU clock cycles, and other related data.

The “sector count” comprises the number of physical sectors on the diskthat are used for this chunk of compressed data. The “LBA” refers to thelogical block address, or physical disk address, for this chunk ofcompressed data.

Referring back to FIG. 4 a, each “Data” block represent each data chunkcomprising a header and compressed data. The data chunk may up anywherefrom 1 to 256 sectors on the disk. Each compressed chunk of data ispreferably preceded on the disk by a data block header that preferablycomprises the following information: (i) sector map; (ii) VBI; (iii) ID(“Magic”) Number; and (iv) checksum.

The “sector map” comprises a copy of the sector map entry in the VBT forthis data chunk. The “VBI” is the Virtual Block Index, which is theindex into the VBT that corresponds to this data chunk. The “ID (“Magic)Number” identifies this data as a data block header. The “checksum”number will change based on the data in the header and is used for errorchecking. This number is preferably chosen such that the addition of allthe words in the header (including the checksum) will equal zero.

It should be noted that the present invention is not limited tochecksums but may employ any manner of error detection and correctiontechniques, utilizing greatly expanded fields error detection and/orcorrection.

It should be further noted that additional fields may be employed tosupport encryption, specifically an identifier for encrypted orunencrypted data along with any parameters necessary for routing orprocessing the data to an appropriate decryption module or user.

The virtual size of the disk will depend on the physical size of thedisk, the compress size selected, and the expected compression ratio.For example, assume there is a 75 GB disk with a selected compress sizeexpecting a 3:1 compression ratio, the virtual disk size would be 225GB. This will be the maximum amount of uncompressed data that the filesystem will be able to store on the disk.

If the number chosen is too small, then the entire disk will not beutilized. Consider the above example where a system comprises a 75 GBdisk and a 225 GB virtual size. Assume that in actuality duringoperation the average compression ratio obtained is 5:1. Whereas thiscould theoretically allow 375 GB to be stored on the 75 GB disk, inpractice, only 225 GB would be able to be stored on the disk before a“disk full” message is received. Indeed, with a 5:1 compression ratio,the 225 GB of data would only take up 45 GB on the disk leaving 30 GBunused. Since the operating system would think the disk is full, itwould not attempt to write any more information to the disk.

On the other hand, if the number chosen is too large, then the disk willfill up when the operating system would still indicate that there wasspace available on the disk. Again consider the above example where asystem comprises a 75 GB disk and a 225 GB virtual size. Assume furtherthat during operation, the average compression ratio actually obtainedis only 2:1. In this case, the physical disk would be full after writing150 GB to it, but the operating system would still think there is 75 GBremaining. If the operating system tried to write more information tothe disk, an error would occur.

Thus, in another embodiment of the present invention, the virtual sizeof the disk is dynamically altered based upon the achieved compressionratio. In one embodiment, a running average may be utilized toreallocate the virtual disk size. Alternatively, certain portions of theratios may already be known—such as a preinstalled operating system andprograms. Thus, this ratio is utilized for that portion of the disk, andpredictive techniques are utilized for the balance of the disk or disks.

Yet in another embodiment, users are prompted for setup information andthe computer selects the appropriate virtual disk(s) size or selects thebest method of estimation based on, e.g., a high level menu of what isthe purpose of this computer: home, home office, business, server.Another submenu may ask for the expected data mix, word, excel, video,music, etc. Then, based upon expected usage and associated compressionratios (or the use of already compressed data in the event of certainforms of music and video) the results are utilized to set the virtualdisk size.

It should be noted that the present invention is independent of thenumber or types of physical or virtual disks, and indeed may be utilizedwith any type of storage.

It is to be understood that the systems and methods described herein maybe implemented in various forms of hardware, software, firmware, specialpurpose processors, or a combination thereof. In particular, the presentinvention may be implemented as an application comprising programinstructions that are tangibly embodied on a program storage device(e.g., magnetic floppy disk, RAM, ROM, CD ROM, etc.) and executable byany device or machine comprising suitable architecture. It is to befurther understood that, because some of the constituent systemcomponents and process steps depicted in the accompanying Figures arepreferably implemented in software, the actual connections between suchcomponents and steps may differ depending upon the manner in which thepresent invention is programmed. Given the teachings herein, one ofordinary skill in the related art will be able to contemplate these andsimilar implementations or configurations of the present invention.

Although illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that thepresent system and method is not limited to those precise embodiments,and that various other changes and modifications may be affected thereinby one skilled in the art without departing from the scope or spirit ofthe invention. All such changes and modifications are intended to beincluded within the scope of the invention as defined by the appendedclaims.

1. A method comprising: providing a throughput threshold for acommunications channel between a first device and a second device;tracking whether a first compressed data provided through saidcommunications channel exceeds said throughput threshold, wherein saidfirst compressed data is provided by a first compression algorithm atsaid first device, said first compressed data is decompressed by a firstdecompression algorithm at said second device, and said firstcompression algorithm and first decompression algorithm are symmetrical;and providing, if said throughput threshold is exceeded by said firstcompressed data, a second compressed data through said communicationschannel, wherein said second compressed data is provided by a secondcompression algorithm at said first device, said second compressed datais decompressed by a second decompression routine at said second device,and said second compression algorithm and second decompression algorithmare asymmetrical.
 2. The method of claim 1, wherein said second devicecomprises a storage device.
 3. The method of claim 1, wherein saidsecond device comprises a random access storage device.
 4. The method ofclaim 1, wherein said second device comprises a non-volatile storagedevice.
 5. The method of claim 1, wherein said second device comprises avolatile storage device.
 6. The method of claim 1, wherein said seconddevice comprises a magnetic disk.
 7. The method of claim 1, wherein saidsecond device comprises an optical disk.
 8. The method of claim 1,wherein said first compression algorithm provides said first compresseddata in real-time.
 9. The method of claim 1, wherein said firstdecompression algorithm operates in real-time.
 10. The method of claim1, wherein said second device comprises a remote device.
 11. The methodof claim 1, wherein said second device comprises a network device. 12.The method of claim 1, wherein the compression ratio of said firstcompressed data is greater than the compression ratio of said secondcompressed data.
 13. The method of claim 1, wherein said secondcompressed data comprises website data.
 14. The method of claim 1,wherein said first compressed data comprises user-generated data. 15.The method of claim 1, wherein said first compressed data comprisesuser-generated document data.
 16. The method of claim 1, wherein saidfirst compressed data comprises user-generated spreadsheet data.
 17. Themethod of claim 1, wherein said second compressed data comprises anapplication.
 18. The method of claim 1, wherein said second compresseddata comprises an operating system.
 19. The method of claim 1, whereinsaid second device comprises a hard disk.